Cooling system for an on-board inert gas generating system

ABSTRACT

The inert gas generating system includes a compressed air source, a cooling air source, and a separation module. The separation module includes first and second inlets and outlets. The first inlet is coupled to the compressed air source. The first outlet is coupled to the first inlet via a bundle of hollow fiber membranes. The second inlet is coupled to the cooling air source, and the second outlet is coupled to the second inlet via a space surrounding the bundle of hollow fiber membranes.

[0001] This patent claims priority pursuant to 35 U.S.C. § 119(e) and §120 to U.S. Provisional Patent Application Ser. No. 60/453,102, filedMar. 7, 2003, the disclosure of which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates generally to cooling systems. Morespecifically, the invention relates to a system and method for cooling anitrogen enriched air stream as it passes through an air separationmodule (ASM) of an On-board Inert Gas Generating Systems (OBIGGS).

[0004] 2. Description of Related Art

[0005] The energy requirements of most modern aircraft are supplied bycombusting aviation gasoline, which is typically stored in fuel tankswithin an aircraft's wings. Such fuel tanks also contain an explosivefuel/air mixture in the area above the fuel, otherwise known as theullage. Accordingly, many systems have been developed to reduce thedanger of accidentally igniting this air/fuel mixture.

[0006] One way of addressing such a danger is to replace the explosiveair/fuel mixture with a nonflammable inert gas, usually nitrogen. TheOn-board Inert Gas Generating System (OBIGGS) does just this, byseparating nitrogen from local, ambient air and replacing the fuel/airmixture in the ullage with this nitrogen.

[0007] Military aircraft have used OBIGGS systems for many years toprotect against fuel tank explosions caused by extreme aircraftoperation and exposure to small arms fire. However, military aircraftare not the only aircraft that would benefit from OBIGGS. For example,investigations into the cause of recent air disasters have concludedthat unknown sources may be responsible for fuel tank ignition andexplosion. Subsequently, OBIGGS has been evaluated as a way to protectcommercial aircraft against such fuel tank explosions caused by anyignition source.

[0008] Prior OBIGGS systems have proved relatively unreliable, heavy,and costly for both initial acquisition and non-military operation.Accordingly, a need exists for a reliable, simple, light, andinexpensive OBIGGS system for commercial aircraft application.

[0009] Moreover, the inert gas introduced into the ullage must be at arelatively low temperature. To ensure that the inert gas is at asufficiently cool temperature, current OBIGGS systems typically pre-coolthe air entering the ASM of the OBIGGS system using bulky and expensiveheat exchangers. Such a heat exchanger is shown in U.S. Pat. No.4,556,180. Accordingly, a system and method for cooling the inert airbefore it is introduced into the ullage, while eliminating the use ofbulky and costly heat exchangers, would be highly desirable.

SUMMARY OF THE INVENTION

[0010] The present invention provides a system and method for reducingthe possibility of combustion in aircraft fuel tanks by replacing air inthe ullage of the fuel tank with an inert gas that has been separatedout from the engine bleed air.

[0011] In one embodiment of the invention there is provided an inert gasgenerating system. The inert gas generating system includes a compressedair source, a cooling air source, and a separation module. Theseparation module includes a housing, multiple hollow fiber membranesdisposed at least partially within the housing, first and second inlets,and first and second outlets. The first inlet is fluidly coupled to thecompressed air source, while the first outlet is fluidly coupled to thefirst inlet via the hollow fiber membranes. The second inlet is fluidlycoupled to the cooling air source, while the second outlet is fluidlycoupled to the second inlet via a space surrounding the hollow fibermembranes. The separation module also preferably includes an on-boardfilter positioned between the first inlet and the hollow fibermembranes. In addition, the inert gas generating system also preferablyincludes a filter positioned between the compressed air source and thefirst inlet. Also, a filter may be positioned between the second inletand the space. In a preferred embodiment, a valve is coupled between thecooling air source and the second inlet. A temperature sensor is alsocoupled between the cooling air source and the second inlet. Thetemperature sensor is configured to control the valve based on atemperature of the cooling air.

[0012] In another embodiment of the invention there is provided a methodfor generating inert gas. Air is firstly compressed into compressed air.Thereafter, the compressed air is introduced into multiple hollow fibermembranes. The compressed air is separated into nitrogen Enriched Air(NEA) within the hollow fiber membranes and oxygen enriched air (OEA) ina space surrounding the hollow fiber membranes. At the same time,cooling air is introduced into the space to cool the NEA within thehollow fiber membranes into cooled NEA. The cooled NEA is then expelledfrom the hollow fiber membranes, and the OEA and the cooling air isexpelled from the space. Accordingly, the present invention enhances theperformance of the system by cooling the NEA flow. This is accomplishedby transferring the heat of the NEA flow to the cooling air flow fromthe external surface of the hollow fibers. This significantly simplifiesthe system and eliminates the need for a separate heat exchanger.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0013] The foregoing and other aspects and advantages of the presentinvention will be better understood from the following detaileddescription when read in conjunction with the drawings, in which:

[0014]FIG. 1 is a schematic view of one embodiment of a modular on-boardinert gas generating system according to the present invention;

[0015]FIG. 2 is a schematic view of an alternative embodiment of theinvention;

[0016]FIG. 2A is a schematic view of a further alternative embodiment ofthe invention;

[0017]FIG. 3 is a cross-sectional view of a modular system according tothe invention;

[0018]FIG. 3A is a cross-sectional view of another modular systemaccording to the invention;

[0019]FIG. 3B is a schematic view of a modular system employing multiplemodules according to the invention;

[0020]FIG. 4 is a perspective view of an embodiment of the invention;

[0021]FIG. 5 is a schematic view of another on-board inert gasgenerating system that includes an air separation module (ASM)incorporating a cooling system, according to another embodiment of theinvention;

[0022]FIG. 6 is a more detailed view of the separation module, as shownand described in relation to FIG. 5; and

[0023]FIG. 7 is a flow chart of a method for obtaining an inert gas froma compressed air stream using the ASM shown in FIGS. 5 and 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] As illustrated in FIG. 1, system 10 according to one embodimentof the invention uses aircraft engine bleed air 12 that is suppliedunder conditions of elevated temperature and elevated pressure togenerate gas for inerting aircraft fuel tanks. It will be appreciated bypersons skilled in the art that the present invention is equally usefulfor inerting cargo holds and other void spaces. Engine bleed air istypically supplied from taps in the compressor section of the aircraftengines at temperatures in the range of 300° F.-400° F. and at pressuresin the range of 10-45 psig depending on compressor rotation speed. It istypically used as a utility source of pressurized air on board aircraft.System 10 operates whenever bleed air is available and, thus, avoids theuse of compressors or complex control valves.

[0025] Bleed air 12 is introduced at one end of system 10 andnitrogen-enriched air (NEA) is produced from the other end. Bleed air 12flows under pressure and temperature to heat exchanger 14. A branchpassage taps off a small portion of the pressurized bleed air to powerjet pump 16. For efficient operation, depending on size, air separationmodule (ASM) 18 typically requires input air temperature less than about200° F. Heat exchanger 14 is therefore used to control the temperatureof the engine bleed air fed into ASM 18. Secondary cooling flow 20 isprovided to heat exchanger 14 for this purpose. Jet pump 16 may beoptionally utilized to provide the cooling flow, which is ventedoverboard at outlet 22. If desired, temperature sensor 24 may bepositioned down stream of the heat exchanger to monitor outputtemperature and control secondary flow 20 and/or jet pump 16 based onthe monitored temperature.

[0026] The pressurized airflow from heat exchanger 14 enters filter 26.Filter 26 may comprise multiple filters, such as a coalescing filter toremove particulate contaminants and moisture, and a carbon filter forremoving hydrocarbons. Line 28 drains removed moisture and directs itoverboard at outlet 22.

[0027] After leaving filter 26, the conditioned air enters ASM 18.Typically, ASM 18 provides a total flow in the range of approximately2-4 lbs./min. Depending on aircraft requirements or other systemlimitations, other sizes of ASM may be selected. Using conventionalhollow-fiber technology, ASM 18 separates the air into oxygen-enrichedair (OEA) and nitrogen-enriched air (NEA). In a preferred embodiment,the ASM provides nitrogen-enriched air at flow rates between about 0.5lbs./min. up to about 2 lbs./min. At the lower flow rates a greaternitrogen purity can be achieved, with oxygen making up only about onepercent by volume of the nitrogen-enriched air. At higher flow rates theoxygen content of the nitrogen-enriched air is typically about nine toten percent by volume. Oxygen-enriched air is piped from ASM 18overboard through outlet 22. Check valve 29 is provided in the overboardOEA line to prevent back-flow. Nitrogen-enriched air produced by ASM 18is directed to the fuel tank and/or cargo hold. Orifice 30 is preferablyprovided downstream of ASM 18 to control the flow rate through the ASM.If desired, a stepped or variable orifice may be provided to controlflow rate as described in greater detail below. Optional oxygen sensor32 may be configured to provide signals representing oxygen content ofthe NEA. Another optional sensor that may be provided is mass airflowsensor 34. This may be an automotive-style hot wire mass-flow sensor.System outlet 36 directs the NEA to the fuel tank ullage and optionallyto aircraft cargo hold as desired.

[0028] In an alternative embodiment illustrated in FIG. 2, engine bleedair first passes through an isolation valve 38. Isolation valve 38permits system 10 a to be isolated from the bleed air and, if desired,may be controlled by signals from temperature sensor 24. In thisembodiment secondary cooling air is provided by an atmospheric inlet orscoop (ram air) 40. Secondary cooling air may also be provided by anNACA scoop. Secondary cooling air passes through temperature modulationvalve 42, which also may be controlled by temperature sensor 24.Alternatively, temperature control of the primary bleed airflow may beachieved through a modulated by-pass flow arrangement (described indetail with reference to FIG. 2A). Secondary cooling air obtained fromscoop 40 typically will have a temperature ranging from about −60° F. to110° F. or greater, depending on the environmental conditionsexperienced by the aircraft. The secondary airflow again passes throughheat exchanger 14, optionally assisted by jet pump 16. Operation offilter 26 and ASM 18 is essentially as described above. In thisexemplary embodiment, an orifice is provided with two steps or as astepped choke valve. For example, a first orifice 44 presents an openingof a first size and second orifice 46 presents an opening of a secondsize. The orifice seen by the NEA flow is determined by orifice selector48, which may be a motor actuated valve. The orifice selector isutilized to control the flow rate as described below. NEA exiting thesystem optionally passes through a first check valve 50, after which itis directed through the fuel tank or cargo hold bulkhead 52. A secondcheck valve 54 may be provided before the NEA is injected into the fueltank or cargo hold.

[0029] The embodiments of the present invention as described above takeadvantage of characteristics of ASM 18 to produce higher purity NEA(lower 02 content) when flow is restricted. Flow may be restricted usingdown stream orifices or back pressure. In the embodiments utilizing thevariable orifices, preferably two different restrictions are used. Othernumbers might be used if warranted by system performance andrequirements. Generally, a high restriction provides low flow and highpurity, and a low restriction provides a higher flow and low purity.These embodiments rely on existing aircraft vent systems to providenormal tank inward and outward venting while mixing the NEA in the tankullage or cargo hold space. A high NEA outlet purity combined with alonger flow time will result in an ullage gas with a higher NEA purity.During the climb and cruise portion of a flight, the high purity (lowflow) NEA is delivered to the fuel tank. This stores a high nitrogenconcentration gas in the fuel tank ullage. During the descent portion ofthe flight, in which more air vents into the fuel tank as altitudedecreases, the orifice is set to provide a lower restriction and higherflow, thus producing a lower purity NEA but at greater volume. However,because high purity NEA is already stored in the fuel tank ullage, airforced in through tank vents during descent simply serves to decreasethe nitrogen purity. When supplemented by the high flow low purity NEAprovided during descent, the ullage maintains a nitrogen puritysufficient to maintain the inert condition. Given the typical commercialflight profile, although the nitrogen level decreases during aircraftdescent, with an appropriately sized system nitrogen levels can bemaintained at an inert level through aircraft landing.

[0030] In further alternative embodiments, the system of the presentinvention may be designed to eliminate components such as sensors,variable orifices and the jet pump, thereby further simplifying thesystem and increasing reliability. In one embodiment, orifices 44 and46, and selector valve 48 are eliminated by sizing the system to meetextreme operating conditions at all times. This may be accomplished bysizing the system to provide sufficient NEA during climb and cruiseoperation, so that the oxygen level in the ullage remains at below acritical level during descent and landing. Typically, the criticaloxygen level will be less than about 10%-14% oxygen, more particularlyless than about 12% oxygen. For example, if a system using the multipleorifices as described above were sized to provide NEA at 0.5 lbs/minwith 1% oxygen during climb and cruise, in eliminating the orifices thesystem may be sized to provide NEA continuously with about 2% oxygen ata slightly higher flow rate. Factors considered include fuel tank sizeand aircraft flight profile. The system is then designed to, in effect,store high purity NEA in the fuel tank ullage so that upon inflow of airduring descent the critical oxygen level is not exceeded before aircraftoperation ceases after landing.

[0031] In another embodiment, jet pump 16 may be eliminated by sizingthe system to rely only on ram air from scoop 40 for secondary coolingflow. This has the advantage of further simplifying the system byremoving another component. This advantage must be balanced with theneed for additional ground service equipment to provide cooling fortesting and maintenance when the aircraft is not in flight.

[0032] Another variation involves the removal of temperature sensor 24and temperature modulation valve 42. In this embodiment, a maximum hottemperature is assumed based on the expected operating conditions. ASM18 is then sized to provide the required purity of NEA based on an inputtemperature at the assumed maximum.

[0033] Oxygen sensor 32 and mass flow sensor 34 also may be eliminatedif system health monitoring is only to be performed on the ground usingground service equipment. These alternatives for reducing systemcomplexity may be employed alone or in any combination. Exact sizing ofthe system in the various alternatives described will depend upon theinerting needs and flight profile of the particular aircraft in whichthe system is to be mounted. A person of ordinary skill in the art willbe able to match the system to the aircraft inerting needs based on thedisclosure contained herein.

[0034] In FIG. 2A, a further alternative embodiment of the inventionuses primary heat exchanger bypass flow control to control thetemperature of the air entering the ASM inlet. Bypass valve 43 controlsthe airflow to heat exchanger 14 by controlling the amount of permittedbypass flow. Bypass valve 43 modulates incrementally between closed,causing all bleed air to flow through heat exchanger 14, and open,allowing the unrestricted bypass of bleed air around heat exchanger 14.The airflow allowed to bypass heat exchanger 14 follows bypass conduit41 to the air conduit upstream of temperature sensor 24 and filter 26.Temperature sensor 24 is, therefore positioned to determine thetemperature of air entering filter 26 and ASM 18. That temperature isused to direct bypass valve 43 to open and allow an appropriate amountof air to flow around heat exchanger 14 so that the temperature of theair entering filter 26 and ASM 18 is within a desired temperature range.Bypass valve 43 is preferably a phase-change direct acting mechanicalsensor and flow control valve. Temperature modulation valve 42 (FIG. 1)and the corresponding control capability are added for additionaltemperature control if desired.

[0035] As also shown in FIG. 2A, filter 26 may include three sections.As previously described, filter 26 may contain a coalescing and solidcontainment HEPA filter section, for removing particles and water, and acarbon filter section for hydrocarbon removal. In this embodiment, thefilter also includes an additional HEPA filter 27, similar to the firstfilter section, to prevent carbon filter bits from flaking off theprevious filter section and traveling to ASM 18. Subcomponentsdownstream of ASM 18 may be eliminated as shown in FIG. 2A to reducecost and complexity. In this embodiment the OEA outlet 76 exits themodule to combine with the cooling airflow downstream of the jet pump16. The filter drainpipe 28 also merges with the cooling airflowdownstream of the jet pump 16, but does so within the modular assembly.The embodiments shown in FIG. 2A are otherwise as described withreference to FIG. 2.

[0036] In a further preferred embodiment of the invention, system 10 isprovided as a modular assembly as shown in FIGS. 3 and 4. In oneembodiment, components such as ASM 18, filters 26 and heat exchanger 14are provided within common housing 60. Alternatively, housing 60 mayencompass only the ASM and filters, with the heat exchanger mountedthereon to form a single modular unit. For example band clamps 62 may beprovided between ASM 18 and filter 26, and filter 26 and heat exchanger14 to secure the components together.

[0037] At the outlet side, NEA outlet port 64 communicates with the fueltank ullage. An upper mounting bracket 66 may be provided for securingthe unit in an appropriate aircraft space. At the inlet side, inlet 68receives engine bleed air 12 and directs it toward heat exchanger 14.Secondary air inlet 70 provides a secondary cooling airflow and outlet72 communicates with overboard outlet 22. Lower mount 74 also may beprovided for securing the unit. As shown in FIG. 4, OEA outlet pipe 76,secondary airflow pipe 78 and filter drainpipe 28 all lead to overboardoutlet 22. Oxygen and mass flow sensors may be provided as part of themodular unit, or separately provided, depending on space andinstallation requirements. Similarly, the orifice and associated controlvalve may be included in the modular system.

[0038] The single-housing design thus facilitates a simple, lightweightconfiguration that minimizes both acquisition, in-service andcertification costs by eliminating many of the sub-components previouslyrequired in such systems. By eliminating sub-components thesingle-housing design will also minimize installation costs whencompared to the current distributed component approach. Thesingle-housing design also improves reliability. In a preferredembodiment, the filter is arranged to be an easily replaceable,disposable cartridge, thereby enhancing maintainability.

[0039]FIG. 3A shows an additional preferred embodiment of a modularassembly with components contained within a housing 60. In thisembodiment, the components are arranged so that heat exchanger 14 isbetween filter 26 and ASM 18. Among other advantages, depending oninstallation requirements, this arrangement provides better access tofilter 26 for maintenance purposes. FIGS. 1 and 2 still describe thefunction of this embodiment, with the internal plumbing of the variousairflows configured to accommodate the component arrangement in FIG. 3A.

[0040] Using the modular approach as described, a module may be designedto provide particular, predetermined NEA flow and multiple modulesemployed to meet higher flow rate requirements. For example, theindividual module may be sized to meet the inerting requirements of aparticular customer's smallest aircraft. For larger aircraft of the samecustomer, instead of redesigning the module, multiple modules areemployed to meet the higher flow rate requirements. In this manner,inventory and maintenance costs are reduced because only one type ofequipment is required to service an entire fleet of aircraft ofdifferent sizes.

[0041]FIG. 3B shows one possible arrangement of a modular assemblyemploying multiple modules. In this embodiment, five housings 60 eachcontain an ASM 18, heat exchanger 14, and filter 26, as depicted ineither of FIG. 3 or 3A. The housings are plumbed together in parallel.Bleed air 12 is provided to each heat exchanger 14 through a singleisolation valve 38 and a manifold 39 a. Similarly, manifold 39 bprovides cooling flow 20 to heat exchanger 14 and manifold 39 c collectsboth the OEA and the post-heat exchanger cooling airflow and directs itoverboard 22. NEA is collected by manifold 39 d and directed to systemoutlet 36 and the fuel tank ullage.

[0042] A further embodiment of the invention boosts system flowperformance by tapping bleed air from the high-pressure segment of theaircraft's air cycle machine (ACM). Aircraft environmental controlsystems often use an air compressor to increase bleed air pressure andtemperature in the ACM. This can be used alone or in conjunction with aturbocharger to apply a significantly higher pressure to the ASM. Thehigher pressure increases the flow and/or purity performance of the ASM,resulting in a smaller and less costly ASM for equivalent systemperformance. Alternatively, for larger aircraft, fewer ASM's may berequired using this embodiment, again resulting in reduced costs andreduced complexity.

[0043] The apparatus and method of the present invention provide a moresatisfactory OBIGGS for a number of reasons. The modular approach to thedesign of the equipment reduces acquisition and installation costs. Thecartridge-style filter with quick-release installation features,together with high OBIGGS reliability due to reduced complexity, alsoreduces operational costs. The methodology of increasing NEA purity inthe tank ullage during cruise, together with increased flow/lower purityNEA injection during descent gives all of the benefits of a traditionalOBIGGS system with a much smaller, lighter, less costly, more reliablesystem.

[0044]FIG. 5 is a schematic view of another on-board inert gasgenerating system 100 that includes a separation module 102 that alsocools the outgoing inert gas. Generally, the temperature of thecompressed air entering the separation module is first lowered, as inertgas introduced into the aircraft's fuel tanks must be at lowtemperatures to avoid additional fuel vaporization. Such fuelvaporization may compound the original problem of having an explosivefuel/air mixture in the ullage. Accordingly, the temperature of thecompressed air is lowered before it enters the separation module. Thetypical source of such compressed air is bleed air that is supplied fromtaps in the compressor section of the aircraft engines at temperaturesin the range of 300° F.-400° F.

[0045] The system 100 eliminates the need for pre-cooling the compressedair before is enters the ASM 102. Rather, the ASM itself acts as a heatexchanger to reduce the temperature of the separated inert gas before itis stored in the aircraft's fuel tanks.

[0046] The separation module 102 preferably includes an on-board filter104 (best seen in FIG. 6) and an on-board ASM 106, as best seen in FIG.6. The on-board filter is similar to filter 26 (FIG. 3A) describedabove. Alternatively, or in addition to the on-board filter 104, aseparate filter 26 may be coupled between the source of the compressedair and the separation module 102, as described above. The separationmodule also preferably includes a first inlet 108, a second inlet 110, afirst outlet 112, and a second outlet 114. The first inlet 108 iscoupled to a compressed air source, such as an aircraft's bleed air 103.The first outlet is preferably coupled to the aircraft fuel tanks orcargo areas.

[0047] The ASM 106 serves to separate inert gas, such as nitrogen, fromthe compressed air, such as oxygen and water vapor. The inert gas isexpelled from the first outlet 112 as shown by arrow 116, toward thefuel tank/s, as described above.

[0048] The second inlet 110 is coupled to a cooling air source. In apreferred embodiment, this cooling air source is the ambient airflowsurrounding the aircraft. This ambient airflow is preferably captured bya scoop 118, such as a NACA scoop. Alternatively, the cooling air may besupplied from a tap into another line 120 that obtains cooling air froma scoop or the like. A temperature sensor 122 measures the temperatureof the cooling air introduced into the second inlet 110. Thistemperature from the temperature sensor 122 is used to control a valve124 disposed between the source of cooling air and the second inlet 110.It should be appreciated that the temperature sensor may be positionedelsewhere, such as at second outlet 114.

[0049] The second outlet 114 is preferably coupled to an ejector 126that expels the remainder of the separated air and the warmer coolingair from the separation module 102. The ejector 126 preferably creates anegative pressure or vacuum at the second outlet 114, thereby drawingcooling air into the second inlet 110, through the space surrounding thehollow fibers 130 (FIG. 6), and out of the second outlet 114. Theejector may be powered by the inlet pressurized air, or by internal orexternal ducting. Alternatively, the second outlet 114 may expel theremainder of the separated air and the warmer cooling air by any othersuitable means.

[0050]FIG. 6 is a more detailed view of the separation module 102 shownand described in relation to FIG. 5. As can be seen more clearly in thisfigure, the compressed air or bleed air is introduced into theseparation module 102 at the first inlet 108. In a preferred embodiment,the on-board filter 104 is positioned between the first inlet 108 andthe ASM 106.

[0051] The ASM 106 preferably includes a bundle of hollow fibermembranes 130 fluidly coupling the first inlet and outlet to oneanother. These hollow fiber membranes 130 are preferably hightemperature hollow fiber membranes that are capable of withstandingtypical bleed air temperatures without requiring pre-cooling. In otherwords, these hollow fiber membranes 130 can withstand and operate intemperatures in excess of 300° F.

[0052] In use, compressed or bleed air flows into the first inlet 108,through the on-board filter 104 and into the hollow fiber membranes 130.As the compressed airflows through the hollow fiber membranes 130,oxygen and water vapor pass through the walls of the hollow fibermembranes 130 into space 132 surrounding each of the hollow fibermembranes 130. Compressed air substantially stripped of oxygen, nowmainly nitrogen, exits the hollow fiber membranes 130 and is expelled asinert gas (or nitrogen enriched air (NEA)) from the separation module102 via the first outlet 112.

[0053] Also in use, cooling air from the cooling air source (describedabove) enters the housing at the second inlet 110. The cooling air thenpasses through the space 132 surrounding each of the hollow fibermembranes 130 and is ultimately expelled from the second outlet 114.This space is defined by the separation module's housing 138, the outerperimeter of each of the hollow fibers and the end walls 134. The inletsand outlets of each of the hollow fiber membranes 130 are substantiallyhermetically sealed from the space 132 surrounding the hollow fibermembranes by the end walls 134.

[0054] The separation module 102 may also include another on-boardfilter 136 for filtering the incoming cooling air prior to the coolingairflow contacting the outside of the hollow fibers 130. Also thepressure within the fibers is generally kept higher than the pressureoutside of the fibers so that separation only occurs in one direction,i.e., from within the fibers to the space surrounding the fibers.Furthermore, it should be noted that the position of the second inlet110 and the second outlet 114 may be reversed. Alternatively, the secondinlet 110 and the second outlet 114 may be positioned anywhere, as longas the second inlet 110 and the second outlet 114 penetrate the housing138 of the separation module 102 between the end walls 134.

[0055] In use, the compressed air is ducted directly into the hollowfiber area within the module, i.e., through the hollow fibers 130,whereas the cooling airflows around the hollow fibers, i.e., flowsthrough the space 132.

[0056]FIG. 7 is a flow chart 150 of a method for obtaining an inert gasfrom a compressed air stream using the ASM 106 shown in FIGS. 5 and 6.Initially, air is compressed at step 152. This is preferablyaccomplished by the aircraft engine's compressor/s and extracted asbleed air. Subsequently, this compressed air is filtered at step 154,preferably by the on-board filter 104 (FIG. 6) and/or the separatefilter 26 (FIG. 6). The filtered compressed air is then introduced intothe hollow fibers 130 (FIG. 6), at step 156. The filtered compressed airis then separated, at step 158, by the hollow fibers 130 (FIG. 6) intooxygen enriched air (OEA) outside of the hollow fibers 130 (FIG. 6),i.e., in the space 132 (FIG. 6), and into nitrogen enriched air (NEA) atthe first outlet 112 (FIG. 6) of the ASM 106 (FIG. 6).

[0057] While the filtered compressed air is being separated, at step158, cooling air is introduced into the second inlet 110 at step 160.Control of the cooling air is regulated by the temperature sensor 122(FIG. 5) and the valve 124 (FIG. 5), with or without a controller. Thiscooling air is preferably filtered by the other on-board filter 136(FIG. 6). The cooling air passes through the space 132 (FIG. 6)surrounding the hollow fibers 130 (FIG. 6), thereby cooling theperimeter of the hollow fibers and mixing with the OEA. This cooling ofthe perimeter of the hollow fibers allows the hollow fibers themselvesto cool the NEA passing through the hollow fibers.

[0058] The cooled NEA is then expelled from the first outlet 112 of theASM 106 at step 150. At the same time, the OEA and now warmer coolingair is expelled from the second outlet 114 at step 162. The NEA is thenpreferably stored or introduced into the aircraft's fuel tanks or cargoareas.

[0059] The flow of cooling air around the hollow fibers may have theadditional benefit of helping “strip” oxygen molecules from the hollowfiber surface, and also aspirate flow of the OEA to the outlet port.This in turn may help increase the efficiency of the fibers, by bothapplying a slight vacuum to the fiber surface, and ducting the OEA awayfrom these surfaces.

[0060] Accordingly, the system 100 (FIG. 5) effectively utilizes thehollow fibers to both separate OEA from the compressed airflow source,and function as a heat exchanger. The input to the module is thereforecompressed air and cooling air, while the output is cooled, filtered dryNEA, and OEA which is diluted in its O₂ concentration by mixing with thecooling airflow. In this way, cool inert gas is provided without theneed for a separate heat exchanger, thereby reducing overall systemcomplexity, size, and cost.

[0061] As the separation module 102 (FIGS. 5 and 6) performs a doubleduty, to both separate and cool the NEA flow, the fuel tank (or otherspace on the aircraft) can be inerted by cool NEA flow without the useof a heat exchanger or temperature control system. The additionalpotential benefit is to increase the efficiency of the separationmodule, due to aspiration of the OEA port, and the enhancement of theflow through the space surrounding the hollow fibers. System safety isalso enhanced by ensuring that cooled NEA (instead of high temperatureNEA) is introduced into the fuel tank or other space, and that OEAdischarge flow is diluted with ambient air.

[0062] The foregoing descriptions of specific embodiments of the presentinvention are presented for purposes of illustration and description.They are not intended to be exhaustive or to limit the invention to theprecise forms disclosed. Obviously many modifications and variations arepossible in view of the above teachings. For example, the separationmodule may include more or less components, such as those includedwithin the area marked by reference numeral 127. The embodiments werechosen and described in order to best explain the principles of theinvention and its practical applications, to thereby enable othersskilled in the art to best utilize the invention and various embodimentswith various modifications as are suited to the particular usecontemplated. Furthermore, the order of steps in the method are notnecessarily intended to occur in the sequence laid out. It is intendedthat the scope of the invention be defined by the following claims andtheir equivalents.

What we claim is:
 1. An inert gas generating system comprising: acompressed air source; a cooling air source; a separation modulecomprising: a housing; a first inlet in said housing, where said firstinlet is fluidly coupled to said compressed air source; a first outletin said housing for expelling inert gas enriched air, where said firstoutlet is fluidly coupled to said first inlet; a second inlet in saidhousing, where said second inlet is fluidly coupled to said cooling airsource; and a second outlet in said housing, where said second outlet isfluidly coupled to said second inlet.
 2. The inert gas generating systemof claim 1, wherein said first inlet is coupled to said first outlet viamultiple hollow fiber membranes.
 3. The inert gas generating system ofclaim 2, wherein said separation module further comprises an on-boardfilter positioned between said first inlet and said multiple hollowfiber membranes.
 4. The inert gas generating system of claim 2, whereinsaid hollow fiber membranes are high temperature hollow fiber membranes.5. The inert gas generating system of claim 2, wherein said multiplehollow fiber membranes extend at least partially through said housing.6. The inert gas generating system of claim 2, wherein said second inletis fluidly coupled to said second outlet through a space surroundingsaid multiple hollow fiber membranes.
 7. The inert gas generating systemof claim 2, wherein said second inlet is fluidly coupled to said secondoutlet through a space formed between said housing and said multiplehollow fiber membranes.
 8. The inert gas generating system of claim 7,further comprising a filter positioned between said second inlet andsaid space.
 9. The inert gas generating system of claim 1, furthercomprising a filter positioned between said compressed air source andsaid first inlet.
 10. The inert gas generating system of claim 1,further comprising: a valve coupled between said cooling air source andsaid second inlet; and a temperature sensor also coupled between saidcooling air source and said second inlet, where said temperature sensoris configured to control said valve based on a temperature of saidcooling air.
 11. The inert gas generating system of claim 1, whereinsaid cooling air source is a scoop.
 12. The inert gas generating systemof claim 1, wherein said compressed air source is bleed air.
 13. Theinert gas generating system of claim 1, further comprising an ejectorcoupled to said second outlet for expelling oxygen enriched air mixedwith warmed cooling air from said separation module.
 14. An inert gasgenerating system comprising: a compressed air source; a cooling airsource; a separation module having: a first inlet fluidly coupled tosaid compressed air source; a first outlet fluidly coupled to said firstinlet via multiple hollow fiber membranes; a second inlet fluidlycoupled to said cooling air source; and a second outlet fluidly coupledto said second inlet via a space surrounding said hollow fibermembranes.
 15. The inert gas generating system of claim 14, wherein saidcompressed air source is bleed air.
 16. The inert gas generating systemof claim 14, further comprising an ejector coupled to said second outletfor expelling oxygen enriched air mixed with warmed cooling air fromsaid separation module.
 17. The inert gas generating system of claim 14,wherein said hollow fiber membranes are high temperature hollow fibermembranes.
 18. An inert gas generating system comprising: a compressedair source; a cooling air source; a separation module comprising: ahousing; at least one hollow fiber membrane disposed at least partiallywithin said housing; a first inlet in said housing, where said firstinlet is fluidly coupled to said compressed air source; a first outletin said housing, where said first outlet is fluidly coupled to saidfirst inlet via said at least one hollow fiber membrane; a second inletin said housing, where said second inlet is fluidly coupled to saidcooling air source; and a second outlet in said housing, where saidsecond outlet is fluidly coupled to said second inlet via a spacesurrounding said at least one hollow fiber membrane.
 19. The inert gasgenerating system of claim 18, wherein said compressed air source isbleed air.
 20. The inert gas generating system of claim 18, furthercomprising an ejector coupled to said second outlet for expelling oxygenenriched air mixed with warmed cooling air from said separation module.21. The inert gas generating system of claim 18, wherein said at leastone hollow fiber membrane is a high temperature hollow fiber membrane.22. An inert gas generating system comprising: a separation modulecomprising: a housing; a first inlet in said housing, wherein said firstinlet is configured to be fluidly coupled to a compressed air source; afirst outlet in said housing configured to expel inert gas enriched air;at least one hollow fiber membrane extending at least partially throughsaid housing and fluidly coupling said first inlet to said first outlet;a second inlet in said housing, wherein said second inlet is configuredto be fluidly coupled to a cooling air source; and a second outlet insaid housing, where said second outlet is fluidly coupled to said secondinlet through a space surrounding each of said hollow fiber membranes.23. The inert gas generating system of claim 22, wherein said compressedair source is bleed air.
 24. The inert gas generating system of claim22, further comprising an ejector coupled to said second outlet forexpelling oxygen enriched air mixed with warmed cooling air from saidseparation module.
 25. The inert gas generating system of claim 22,wherein said hollow fiber membranes are a high temperature hollow fibermembranes.
 26. A method for generating inert gas comprising: compressingair into compressed air; introducing said compressed air into multiplehollow fiber membranes; separating said compressed air into nitrogenEnriched Air (NEA) within said hollow fiber membranes and OxygenEnriched Air (OEA) in a space surrounding said multiple hollow fibermembranes; injecting cooling air into said space to cool said NEA withinsaid hollow fiber membranes into cooled NEA; and expelling said cooledNEA from said hollow fiber membranes.
 27. The method of claim 26,wherein said compressing comprises compressing ambient air using acompressor of an aircraft engine.
 28. The method of claim 26, furthercomprising, prior to said introducing, filtering said compressed air.29. The method of claim 26, further comprising, prior to said injecting,filtering said cooling air.
 30. The method of claim 26, furthercomprising storing said NEA.
 31. The method of claim 26, furthercomprising introducing said NEA into an aircraft fuel tank.